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1 // Copyright 2012 the V8 project authors. All rights reserved.
2 // Redistribution and use in source and binary forms, with or without
3 // modification, are permitted provided that the following conditions are
4 // met:
5 //
6 //     * Redistributions of source code must retain the above copyright
7 //       notice, this list of conditions and the following disclaimer.
8 //     * Redistributions in binary form must reproduce the above
9 //       copyright notice, this list of conditions and the following
10 //       disclaimer in the documentation and/or other materials provided
11 //       with the distribution.
12 //     * Neither the name of Google Inc. nor the names of its
13 //       contributors may be used to endorse or promote products derived
14 //       from this software without specific prior written permission.
15 //
16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 
28 #ifndef V8_DATE_H_
29 #define V8_DATE_H_
30 
31 #include "allocation.h"
32 #include "globals.h"
33 #include "platform.h"
34 
35 
36 namespace v8 {
37 namespace internal {
38 
39 class DateCache {
40  public:
41   static const int kMsPerMin = 60 * 1000;
42   static const int kSecPerDay = 24 * 60 * 60;
43   static const int64_t kMsPerDay = kSecPerDay * 1000;
44 
45   // The largest time that can be passed to OS date-time library functions.
46   static const int kMaxEpochTimeInSec = kMaxInt;
47   static const int64_t kMaxEpochTimeInMs =
48       static_cast<int64_t>(kMaxInt) * 1000;
49 
50   // The largest time that can be stored in JSDate.
51   static const int64_t kMaxTimeInMs =
52       static_cast<int64_t>(864000000) * 10000000;
53 
54   // Conservative upper bound on time that can be stored in JSDate
55   // before UTC conversion.
56   static const int64_t kMaxTimeBeforeUTCInMs =
57       kMaxTimeInMs + 10 * kMsPerDay;
58 
59   // Sentinel that denotes an invalid local offset.
60   static const int kInvalidLocalOffsetInMs = kMaxInt;
61   // Sentinel that denotes an invalid cache stamp.
62   // It is an invariant of DateCache that cache stamp is non-negative.
63   static const int kInvalidStamp = -1;
64 
DateCache()65   DateCache() : stamp_(0) {
66     ResetDateCache();
67   }
68 
~DateCache()69   virtual ~DateCache() {}
70 
71 
72   // Clears cached timezone information and increments the cache stamp.
73   void ResetDateCache();
74 
75 
76   // Computes floor(time_ms / kMsPerDay).
DaysFromTime(int64_t time_ms)77   static int DaysFromTime(int64_t time_ms) {
78     if (time_ms < 0) time_ms -= (kMsPerDay - 1);
79     return static_cast<int>(time_ms / kMsPerDay);
80   }
81 
82 
83   // Computes modulo(time_ms, kMsPerDay) given that
84   // days = floor(time_ms / kMsPerDay).
TimeInDay(int64_t time_ms,int days)85   static int TimeInDay(int64_t time_ms, int days) {
86     return static_cast<int>(time_ms - days * kMsPerDay);
87   }
88 
89 
90   // Given the number of days since the epoch, computes the weekday.
91   // ECMA 262 - 15.9.1.6.
Weekday(int days)92   int Weekday(int days) {
93     int result = (days + 4) % 7;
94     return result >= 0 ? result : result + 7;
95   }
96 
97 
IsLeap(int year)98   bool IsLeap(int year) {
99     return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
100   }
101 
102 
103   // ECMA 262 - 15.9.1.7.
LocalOffsetInMs()104   int LocalOffsetInMs() {
105     if (local_offset_ms_ == kInvalidLocalOffsetInMs)  {
106       local_offset_ms_ = GetLocalOffsetFromOS();
107     }
108     return local_offset_ms_;
109   }
110 
111 
LocalTimezone(int64_t time_ms)112   const char* LocalTimezone(int64_t time_ms) {
113     if (time_ms < 0 || time_ms > kMaxEpochTimeInMs) {
114       time_ms = EquivalentTime(time_ms);
115     }
116     return OS::LocalTimezone(static_cast<double>(time_ms));
117   }
118 
119   // ECMA 262 - 15.9.5.26
TimezoneOffset(int64_t time_ms)120   int TimezoneOffset(int64_t time_ms) {
121     int64_t local_ms = ToLocal(time_ms);
122     return static_cast<int>((time_ms - local_ms) / kMsPerMin);
123   }
124 
125   // ECMA 262 - 15.9.1.9
ToLocal(int64_t time_ms)126   int64_t ToLocal(int64_t time_ms) {
127     return time_ms + LocalOffsetInMs() + DaylightSavingsOffsetInMs(time_ms);
128   }
129 
130   // ECMA 262 - 15.9.1.9
ToUTC(int64_t time_ms)131   int64_t ToUTC(int64_t time_ms) {
132     time_ms -= LocalOffsetInMs();
133     return time_ms - DaylightSavingsOffsetInMs(time_ms);
134   }
135 
136 
137   // Computes a time equivalent to the given time according
138   // to ECMA 262 - 15.9.1.9.
139   // The issue here is that some library calls don't work right for dates
140   // that cannot be represented using a non-negative signed 32 bit integer
141   // (measured in whole seconds based on the 1970 epoch).
142   // We solve this by mapping the time to a year with same leap-year-ness
143   // and same starting day for the year. The ECMAscript specification says
144   // we must do this, but for compatibility with other browsers, we use
145   // the actual year if it is in the range 1970..2037
EquivalentTime(int64_t time_ms)146   int64_t EquivalentTime(int64_t time_ms) {
147     int days = DaysFromTime(time_ms);
148     int time_within_day_ms = static_cast<int>(time_ms - days * kMsPerDay);
149     int year, month, day;
150     YearMonthDayFromDays(days, &year, &month, &day);
151     int new_days = DaysFromYearMonth(EquivalentYear(year), month) + day - 1;
152     return static_cast<int64_t>(new_days) * kMsPerDay + time_within_day_ms;
153   }
154 
155   // Returns an equivalent year in the range [2008-2035] matching
156   // - leap year,
157   // - week day of first day.
158   // ECMA 262 - 15.9.1.9.
EquivalentYear(int year)159   int EquivalentYear(int year) {
160     int week_day = Weekday(DaysFromYearMonth(year, 0));
161     int recent_year = (IsLeap(year) ? 1956 : 1967) + (week_day * 12) % 28;
162     // Find the year in the range 2008..2037 that is equivalent mod 28.
163     // Add 3*28 to give a positive argument to the modulus operator.
164     return 2008 + (recent_year + 3 * 28 - 2008) % 28;
165   }
166 
167   // Given the number of days since the epoch, computes
168   // the corresponding year, month, and day.
169   void YearMonthDayFromDays(int days, int* year, int* month, int* day);
170 
171   // Computes the number of days since the epoch for
172   // the first day of the given month in the given year.
173   int DaysFromYearMonth(int year, int month);
174 
175   // Cache stamp is used for invalidating caches in JSDate.
176   // We increment the stamp each time when the timezone information changes.
177   // JSDate objects perform stamp check and invalidate their caches if
178   // their saved stamp is not equal to the current stamp.
stamp()179   Smi* stamp() { return stamp_; }
stamp_address()180   void* stamp_address() { return &stamp_; }
181 
182   // These functions are virtual so that we can override them when testing.
GetDaylightSavingsOffsetFromOS(int64_t time_sec)183   virtual int GetDaylightSavingsOffsetFromOS(int64_t time_sec) {
184     double time_ms = static_cast<double>(time_sec * 1000);
185     return static_cast<int>(OS::DaylightSavingsOffset(time_ms));
186   }
187 
GetLocalOffsetFromOS()188   virtual int GetLocalOffsetFromOS() {
189     double offset = OS::LocalTimeOffset();
190     ASSERT(offset < kInvalidLocalOffsetInMs);
191     return static_cast<int>(offset);
192   }
193 
194  private:
195   // The implementation relies on the fact that no time zones have
196   // more than one daylight savings offset change per 19 days.
197   // In Egypt in 2010 they decided to suspend DST during Ramadan. This
198   // led to a short interval where DST is in effect from September 10 to
199   // September 30.
200   static const int kDefaultDSTDeltaInSec = 19 * kSecPerDay;
201 
202   // Size of the Daylight Savings Time cache.
203   static const int kDSTSize = 32;
204 
205   // Daylight Savings Time segment stores a segment of time where
206   // daylight savings offset does not change.
207   struct DST {
208     int start_sec;
209     int end_sec;
210     int offset_ms;
211     int last_used;
212   };
213 
214   // Computes the daylight savings offset for the given time.
215   // ECMA 262 - 15.9.1.8
216   int DaylightSavingsOffsetInMs(int64_t time_ms);
217 
218   // Sets the before_ and the after_ segments from the DST cache such that
219   // the before_ segment starts earlier than the given time and
220   // the after_ segment start later than the given time.
221   // Both segments might be invalid.
222   // The last_used counters of the before_ and after_ are updated.
223   void ProbeDST(int time_sec);
224 
225   // Finds the least recently used segment from the DST cache that is not
226   // equal to the given 'skip' segment.
227   DST* LeastRecentlyUsedDST(DST* skip);
228 
229   // Extends the after_ segment with the given point or resets it
230   // if it starts later than the given time + kDefaultDSTDeltaInSec.
231   inline void ExtendTheAfterSegment(int time_sec, int offset_ms);
232 
233   // Makes the given segment invalid.
234   inline void ClearSegment(DST* segment);
235 
InvalidSegment(DST * segment)236   bool InvalidSegment(DST* segment) {
237     return segment->start_sec > segment->end_sec;
238   }
239 
240   Smi* stamp_;
241 
242   // Daylight Saving Time cache.
243   DST dst_[kDSTSize];
244   int dst_usage_counter_;
245   DST* before_;
246   DST* after_;
247 
248   int local_offset_ms_;
249 
250   // Year/Month/Day cache.
251   bool ymd_valid_;
252   int ymd_days_;
253   int ymd_year_;
254   int ymd_month_;
255   int ymd_day_;
256 };
257 
258 } }   // namespace v8::internal
259 
260 #endif
261